1. Field of the Invention
This invention relates to a compact variable magnification copying apparatus using an in-mirror lens.
2. Description of the Prior Art
Among copying apparatus, there are those which use a transmission type lens as the image forming lens and those which use a reflection type, so-called in-mirror lens as the image forming lens.
The use of an in-mirror lens has the following advantages over the use of a transmission type lens:
1. The number of lenses constructed is one half of that of a transmission type lens;
2. The error of optical performance resulting from the errors in spatial arrangement of the lens (eccentricity and fall-down of the lens) tends to be cancelled when light is incident on the lens and when light is reflected and thus, a relatively great tolerance of the spatial arrangement of the lens is acceptable;
3. The mirror of the in-mirror lens serves also as the mirror which is provided in the optical path when a transmission type lens is used and therefore, the optical system can be made compact in the horizontal direction;
4. As compared with the transmission type lens, the in-mirror lens is one half the size thereof, thus economizing the space; and
5. The assembly and adjustment of a copying apparatus using an in-mirror lens is very easy and such effect is particularly great in the adjustment for absorbing any irregularity of the focal length.
As a variable magnification copying apparatus which uses an in-mirror lens and in which the object point position of a principal light ray is fixed irrespective of magnification change, there is known the apparatus as disclosed in U.S. Pat. No. 4,040,733, but in this apparatus, the optical axis of the in-mirror lens is parallel to the original carriage and this patent does not disclose a system in which the optical axis of the in-mirror lens is non-parallel to the original carriage, although this is considered to be effective to make the apparatus compact.
Generally, if the angle of view is made small in an in-mirror lens system, vertical compactness of the apparatus may be achieved, but if the optical axis of the in-mirror lens is parallel to the original carriage, the light rays impinging from a first movable mirror onto a second movable mirror tend to be kicked by the in-mirror lens barrel and thus, making the apparatus compact has been difficult.
U.S. Pat. No. 4,040,733 discloses that in a system having two movable mirrors on the object side, the mirror on the image side is displaced with the in-mirror lens during magnification change, whereas this requires the driving system for the mirror on the image side in addition to the slit scanning exposure driving system for the mirror on the object side and has not been favorable to make the apparatus compact.
U.S. Pat. No. 4,027,963 discloses a reduction copying system in which the optical axis of the in-mirror lens is non-parallel to the original carriage, but this is merely a system capable of reduction copying only in sheet mode with the aid of a mirror additionally provided. U.S. Pat. No. 4,053,221 merely discloses a reduction copying system available only in the sheet mode using lens interchange. U.S. Pat. No. 4,084,897 also discloses a reduction copying system in which the optical axis of the in-mirror lens is non-parallel to the original carriage, but this has suffered from a problem that during magnification change, the object point position of a principal light ray on the original surface is displaced and not fixed, so that the initial position of the slit exposure scanning differs.